1. Field of the Invention
The present invention relates to sealing devices and, more particularly, to seals, packings and the like used in environments wherein at least a portion of the sealing device is subjected to extrusion forces. Typically such forces are experienced by down hole oil tools. For example, in the application of a down hole packer, the area between the oil tool and the well casing is sealed.
2. Description of the Prior Art
Sealing devices, such as seals or packings, whether of the dynamic or static type, are usually made, or have portions made of materials which, to some extent, are resilient or at least deformable. In order to seal effectively, it is usually necessary that the sealing device be placed under some compressive loading between the components of the assembly to be sealed. Because of the compressive load and the deformable nature of at least a portion of the seal, if the seal is subjected to sufficient pressure, there is a tendency for portions of the seal to be subjected to extrusion forces which will either distort the seal and impair its effectiveness as a seal or, in more severe cases, force portions of the seal into clearances between the components to be sealed.
In an attempt to overcome this extrusion problem, workers in the field have resorted to various techniques. One common practice employed to prevent such extrusion as, for example in a seal ring or packing used between relatively reciprocating or rotating parts, is to mount separate back-up rings or washes adjacent a set of seal ring, the back-up rings serving to prevent the outer seal rings from being extruded. These back-up rings are generally made of metal or other hard materials which generally must be machined or are made of bare metal mesh. Another technique which has been used is shown in U.S. Pat. No. 3,094,337 wherein there are disclosed anti-extrusion seal rings in which an annulus of a relatively soft sealing material is bonded to annular sections of anti-extrusion materials such as thermosetting resins or the like.